Method and system for wireless local area network (wlan) phase shifter training   

Abstract: Aspects of a method and system for wireless local area network (WLAN) phase shifter training are presented. Aspect of the system may enable a receiving station, at which is located a plurality of receiving antennas, to estimate the relative phase at which each of the receiving antennas receives signals from a transmitting station. This process may be referred to as phase shifter training. After determining the relative phase for each of the receiving antennas, the receiving station may process received signals by phase shifting the signals received via each of the receiving antennas in accordance with the relative phase shifts determined during the phase shifter training process. Signals received via a selected one of the receiving antennas may be unshifted. The processed signals may be combined to generate a diversity reception signal.

CROSS-REFERENCE TO RELATED APPLICATIONS

Not Applicable.

FIELD OF THE INVENTION

Certain embodiments of the invention relate to data communication. More specifically, certain embodiments of the invention relate to a method and system for wireless local area network (WLAN) phase shifter training.

BACKGROUND OF THE INVENTION

Wireless local area network (WLAN) systems enable the communication of data via a wireless communication medium by, for example, transmitting radio frequency (RF) signals that carry data between a transmitting station and a receiving station. A range of frequencies, referred to as the WLAN frequency spectrum, may be utilized for communication between stations in a WLAN system. The frequency spectrum may be divided into RF channels wherein each RF channel represented an assigned frequency within the WLAN frequency spectrum. Each RF channel may, in turn, comprise a range of frequencies referred to as an RF channel bandwidth. Each RF channel within the WLAN frequency spectrum may comprise a range of frequencies, which is non-overlapping and distinct from other RF channels.

In a typical WLAN setting there are various objects present in addition to the transmitting station and the receiving station. The transmitting station transmits data to the receiving station via data symbols, which are transmitted via a transmitted signal. The transmitted signal may comprise a one or more frequency carrier signals (wherein each frequency carrier signal is associated with a distinct frequency within a given RF channel bandwidth), which are utilized to generate a corresponding one or more carrier-modulated signals to enable the transport of the data symbols via the wireless communication medium. The time interval, beginning at the time instant at which the transmitting station begins transmission one or more current data symbols via the one or more frequency carrier signals, and ending at the time instant at which the transmitting station begins transmission of a subsequent one or more data symbols may be referred to as a symbol period.

Signals transmitted by the transmitting stations typically experience a natural expansion of the radio wave front as the signals propagate in the wireless communication medium. Portions of the expanding signal often interact with the various objects present in the WLAN setting and are, in many cases, reflected off the various objects. The reflected signal portions may continue propagating in the wireless communication medium. One or more portions of a transmitted signal may experience multiple reflections while propagating through the wireless communication medium. Each of the one or more portions of the transmitted signal is referred to as a multipath signal. The path traveled by a multipath signal may be referred to as a signal path.

A plurality of multipath signals may be received at the receiving station. The multipath signals may comprise a line of sight (LOS) signal, which is transmitted from the transmitting station, via the wireless communication medium, to the receiving station without encountering reflections. In addition, the multipath signals may comprise one or more signals, which encounter one or more reflections while propagating from the transmitting station to the receiving station via the wireless communication medium. The various multipath signals, which are received at the receiving station, may arrive at different time instants. The time interval, beginning at the time instant at which the first of the multipath signals arrives at the receiving station and ending at the time instant at which the last of the multipath signals arrives at the receiving station is referred to as a delay spread.

In addition to delay spread that results from multiple signal paths, there may also be a delay spread within a given signal path. For example, in WLAN systems, which utilize orthogonal frequency division multiplexing (OFDM), an OFDM symbol may be generated by concurrently transmitting individual data symbols via a plurality of concurrently transmitted frequency carrier signals. Delay spread may occur within a given signal path when some of the frequency carrier signals within an RF channel bandwidth propagate through the wireless communication medium at different speed(s) relative to other frequency carrier signals. The delay spread may be utilized to determine the coherence bandwidth for the RF channel.

Signals, which are transmitted from a transmitting station to a receiving station, are typically subjected to distortion as they are propagated through the wireless communication medium. Consequently, the receiving station may receive a distorted version of the signals transmitted by the transmitting station. The distortion of transmitted signals is referred to as fading. Two types of fading are flat fading and frequency selective fading. Flat fading may occur when the delay spread is less than the symbol period, or correspondingly, when the signal bandwidth for the RF channel is less than the coherence bandwidth. In a flat fading RF channel, amplitude fading may be a contributor to the signal fading in the RF channel. Amplitude fading refers to the tendency of signals to attenuate as they are propagated through a wireless communication medium. Frequency selective fading may occur when the delay spread is greater than the symbol period, or correspondingly, when the signal bandwidth for the RF channel is greater than the coherence bandwidth. In a frequency selective fading RF channel, intersymbol interference may be a contributor to signal fading in the RF channel. Intersymbol interference refers to an occurrence in which a receiving station begins to receive signals for a current one or more transmitted data symbols while still receiving signals from a previous one or more transmitted data symbols.

Further limitations and disadvantages of conventional and traditional approaches will become apparent to one of skill in the art, through comparison of such systems with some aspects of the present invention as set forth in the remainder of the present application with reference to the drawings.

SUMMARY

A method and system for wireless local area network (WLAN) phase shifter training, substantially as shown in and/or described in connection with at least one of the figures, as set forth more completely in the claims.

These and other advantages, aspects and novel features of the present invention, as well as details of an illustrated embodiment thereof, will be more fully understood from the following description and drawings.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is an exemplary wireless communication system, which may be utilized in connection with an embodiment of the invention.

FIG. 2 is an exemplary transceiver comprising a plurality of transmitting antennas and a plurality of receiving antennas, which may be utilized in connection with an embodiment of the invention.

FIG. 3 is an illustration exemplary transmitted data unit in a WLAN, which may be utilized in connection with an embodiment of the invention.

FIG. 4A is an exemplary diagram illustrating phase shifter training for equal phase received signals, in accordance with an embodiment of the invention.

FIG. 4B is an exemplary diagram illustrating phase shifter training for unequal phase received signals, in accordance with an embodiment of the invention.

FIG. 5 is a flowchart illustrating exemplary steps for phase shifter training, in accordance with an embodiment of the invention.

DETAILED DESCRIPTION

Certain embodiments of the invention may be found in a method and system for wireless local area network (WLAN) phase shifter training. Various embodiments of the invention comprise a system, which enables a receiving station, at which is located a plurality of receiving antennas, to estimate the relative phase at which each of the receiving antennas receives signals from a transmitting station. This process may be referred to as phase shifter training. After determining the relative phase for each of the receiving antennas, the receiving station may process received signals by phase shifting the signals received via each of the receiving antennas in accordance with the relative phase shifts determined during the phase shifter training process. In various embodiments of the invention, signals received via a selected one of the receiving antennas may be unshifted. The processed signals may be combined to generate a diversity reception signal.

FIG. 1 is an exemplary wireless communication system, which may be utilized in connection with an embodiment of the invention. Referring to FIG. 1, there is shown an access point (AP) 102, a wireless local area network (WLAN) station (STA) 104, and a network 108. The AP 102 and the STA 104 may communicate wirelessly via one or more radio frequency (RF) channels 106a and 106b. The AP 102 and STA 104 may each comprise a plurality of transmitting antennas and/or receiving antennas. As shown in FIG. 1, the AP comprises a single transmitting antenna 112, and the STA 104 comprises a plurality of receiving antennas 114a and 114b. The AP 102 may be communicatively coupled to the network 108. The AP 102, STA 104 and network 108 may enable communication based on one or more IEEE 802 standards, for example IEEE 802.11.

The STA 104 may utilize a plurality of RF channels 106a and 106b to receive signals from the AP 102. The AP 102 may utilize the transmitting antenna 112 to transmit signals, which may be received at the STA 104, via RF channel 106a at receiving antenna 114a, and via RF channel 106b at receiving antenna 114b. The signals received via RF channels 106a and 106b may comprise one of more frequencies associated with a channel as determined by a relevant standard, such as IEEE 802.11.

In operation, the STA 104 may receive a plurality of multipath signals via the RF channels 106a and 106b . The multipath signals may be generated based on the transmission of signals by the AP 102. At least a portion of the multipath signals may be received at the STA 104 via RF channel 106a and a subsequent portion of the multipath signals may be received via RF channel 106b . Depending upon the relative positions of the AP 102 and the STA 104, the length of the signal path for a signal received via receiving antenna 114a may differ from the length of the corresponding signal path for the signal received via receiving antenna 114b. For example, for a LOS signal, the length of the signal path from the transmitting antenna 112 to the receiving antenna 114a may be referred to as d1, while the length of the signal path from the transmitting antenna 112 to the receiving antenna 114b may be referred to as d2. In instances when d1≠d2 there may be a relative phase shift between the LOS signal received at receiving antenna 114a and the LOS signal received at receiving antenna 114b.

For an RF signal, s(t), transmitted by the AP 102, which may be represented as shown in the following equation:

s(t)=Re{A(t)·ej·ωt·t}  [1]

where ωt refers to the carrier frequency generated by AP 102, t represents time, A(t) represents the baseband signal transmitted by the AP 102, and j represents √{square root over (−1)}.

Given the RF signal s(t) as shown in equation [1], the LOS RF signal received at the STA 104 via receiving antenna 114a, r1(t), may be represented as shown in the following equation:

r 1  ( t ) ≈ h 1 · Re  { A  ( t ) ·  j · [ ω t · ( t + d 1 C ) ] } + η 1 [ 2 ]

where h1 refers to the attenuation of the RF channel 106a, d1 refers to the length of the signal path from the transmitting antenna 112 to the receiving antenna 114a, C refers to the velocity of propagation of RF signal via RF channel 106a and η1 refers to the thermal noise generated by antenna 114a.

The LOS signal received at the STA 104 via receiving antenna 114b, r2(t), may be represented as shown in the following equation:

r 2  ( t ) ≈ h 2 · Re  { A  ( t ) ·  j · [ ω t · ( t + d 2 C ) ] } + η 2 [ 3 ]

where h2 refers to the attenuation of the RF channel 106b , d2 refers to the length of the signal path from the transmitting antenna 112 to the receiving antenna 114b, C refers to the velocity of propagation of RF signal via RF channel 106b and η2 refers to the thermal noise generated by antenna 114b.

The relative phase shift between signal r1(t) received via antenna 114a and signal r2(t) received via antenna 114b may be represented as shown in the following equation:

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